Research has been focused on high efficiency thermoelectric materials in the field of thermoelectric technology. Properties of thermoelectric materials are defined as a di-mensionless figure of merit (ZT).
                    ZT        =                                            S              2                        ⁢            σ            ⁢                                                  ⁢            T                    k                                    Equation        ⁢                                  ⁢        1            
In Equation 1, S represents Seebeck coefficient, a represents electrical conductivity, ϰrepresents thermal conductivity, and T represents absolute temperature.
As the Seebeck coefficient and electrical conductivity increase and the thermal conductivity decreases, the ZT increases. The thermal conductivity is defined as a sum of a thermal conductivity obtained from electron transfer according to the Wiedemann-Franz law and a thermal conductivity obtained from lattice vibration of a material.
Si-Te-based thermoelectric materials having excellent thermoelectric properties at a temperature of 300° C. or less have not been widely used due to high manufacturing costs, high brittleness, high density, and difficulty in shaping. Thus, carbonaceous materials have been used as thermoelectric materials to improve these properties. Although carbon nanotubes and graphene have excellent electrical properties, commercialization thereof is limited due to high manufacturing costs, difficulty in conversion from a p-type thermoelectric material to an n-type thermoelectric material, and high thermal conductivity.
Also, thermoelectric devices including a thermoelectric material using a general inorganic material cannot be applied to various apparatuses due to high density, high weight, and low flexibility.
Thus, there is still a need to develop a thermoelectric material having a structure with improved thermoelectric properties suitable for various apparatuses.
Also, to increase the efficiency of a thermoelectric module for power conversion, various factors such as contact resistance of elements in the thermoelectric module and the number of thermoelectric pairs including n-type and p-type thermoelectric semi-conductors need to be considered.
The ZT may increase as contact resistance decreases and the number of thermoelectric pairs increases, resulting in an increase in efficiency of the thermoelectric module.
In the thermoelectric module, electricity flows from a high-temperature insulating plate to a low-temperature insulating plate via an electrode, the thermoelectric material, and the electrode. Thus, an adhesion process of these elements needs to be performed to reduce electrical resistance to obtain high current density and thermoelectric efficiency of the thermoelectric module.
Therefore, there is still a need to develop methods of preparing thermoelectric materials to increase current density and thermoelectric efficiency of thermoelectric modules.